I think EcoPro is best described as "anti-sport" mode. The quirkiest thing about Eco mode is that there's more resistance to the gas pedal. In heavy traffic and slow city driving (like where I live in DC) I think it'll save me a couple mpgs. The cool thing is that it actually calculates how many mgs you've saved. Now with that said - I didn't buy a BMW (especially a 35i) for it's fuel economy, but with premium flirting at $5/gallon...why not from time to time?
The start/stop operation is strange but I think I'll get used to it pretty fast. There's a very brief delay but hardly long enough to notice. With as much as I stop in traffic around DC I think I'll end appreciating it, if only for the the fuel cost savings. Of course, if you don't like it you can always shut it off (control is by the ignition); however, you'd have to do so every time. Enjoy!